1. Field of the Invention
The present invention relates to methods of vaporizing liquids, and more particularly, to a method of vaporizing a multicomponent liquid.
2. Description of the Prior Art
Hawkinson, et al. U.S. Pat. No. 2,491,732 which issued on Dec. 29, 1949, describes a method of vaporizing hydrogen peroxide. The liquid is sprayed in the form of finely divided droplets onto the walls of a vaporizer which are coated with a nonvolatile stabilizer for hydrogen peroxide and heated sufficiently to rapidly and completely vaporize the liquid sprayed onto the walls. The heated walls of the vaporizer must be inclined from the horizontal to ensure formation of a hydrogen peroxide film on the walls of the vaporizer.
The Hawkinson method is not compatable with sterilizer applications. A relatively large surface area is required to provide the desired efficiency. The vapor is transferred to another location for ultimate use. Although evaporation of the hydrogen peroxide and water is simultaneous in the vaporizer, the water vapor travels faster than the hydrogen peroxide vapor, thus the vapors reaching the area of end use are not in the same concentration as the initial solution.
U.S. Pat. Nos. 4,169,123 and 4,169,124 to Moore et al. and Forstrom et al., respectively, describe sterilization techniques using gaseous hydrogen peroxide. A hydrogen peroxide and water solution is vaporized in a closed sterilization chamber. The vapors are permitted to contact the items to be sterilized to achieve sterilization.
In these prior art sterilizer methods, water is vaporized more quickly than hydrogen peroxide and thus, the water vapor reaches the items to be sterilized first and in higher concentrations. The water vapor becomes an effective barrier to hydrogen peroxide penetration around small crevices and lumens of the items in the sterilizer.
When vaporizing multicomponent liquids, particularly those having components of significantly differing boiling points, the more volatile liquid will vaporize first. According to Raoult's Law, the vapor pressure of a component in a binary solution is equal to its pure vapor pressure multiplied by the mole fraction of a particular constituent. For nonideal solutions, an activity coefficient must also be factored in. Thus, EQU P.sub.A =X.sub.A P.sub.A .degree..gamma.A
Where
P.sub.A is the vapor pressure of component A; PA1 X.sub.A is equal to the mole fraction of A in the mixture; PA1 P.sub.A .degree. is the vapor pressure of pure A; and PA1 .gamma..sub.A is the activity coefficient for A in the solution.
Where A is, for example, hydrogen peroxide in a water solution, the pure vapor pressure of water is greater than that of peroxide, thus, the vapor pressure of the water component in the binary solution will be greater than that of the peroxide unless the mole fraction of peroxide in the solution becomes very large. The handling requirements for highly concentrated hydrogen peroxide solutions are so onerous because of the hazardous nature of the peroxide that maintaining such solutions is impractical.
There is a need for a method of vaporizing multicomponent liquids, particularly those having components of significantly differing volatilities, which provides a multicomponent vapor of substantially the same percent weight composition as the multicomponent liquid which is compatible with sterilizer practice. There is a further need for such a method which will permit the use of safe concentrations of the constituent components.